The present invention relates generally to heat pump and air-conditioning systems (HVAC systems). More particularly, the invention relates to an improved forced air system in which the indoor fan speed is variably controlled based on measured liquid refrigerant temperature.
Heat pump and air-conditioning systems have become quite sophisticated in recent years, due in part to the desire for high efficiency and improved occupant comfort. Many of today's control systems for heat pumps and air conditioners use microprocessor-based electronics with a wide assortment of temperature, pressure and humidity sensors. On the one hand, these microprocessor-based systems, with multiple diverse sensors, are quite versatile and are far better able to optimize efficiency and occupant comfort than worthy simple systems of the past. On the other hand, microprocessor-based systems are becoming increasingly complex.
By way of example, U.S. Pat No. 5,303,561 to Bahel et al., entitled "Control System for Heat Pump Having Humidity Responsive Variable Speed Fan," issued Apr. 19, 1994, a microprocessor-based control system is described. That patent is assigned to the assignee of the present invention. It describes a system which controls indoor fan speed based on humidity measurements, to produce a slower airflow when conditions are humid, in order to help remove moisture from the air.
By way of further example, U.S. Pat. No. 5,303,562 to Bahel et al. entitled "Control System for Heat Pump/Air-Conditioning System for Improved Cyclic Performance," issued Apr. 19, 1994, another microprocessor-based control system is described. This patent is also assigned to the assignee of the present invention. It describes a system which optimizes efficiency of the ON/OFF refrigeration cycle. Indoor fan speed is controlled by a proportional electrical signal driving a variable speed motor to optimize airflow in relation to the temperature of the heat exchanging elements. Both of these systems employ a plurality of temperature sensors and a humidity sensor.
The present invention seeks to retain the advantages of microprocessor-based technology, particularly with regard to forced airflow control. Departing from the technology of the past, however, the present invention seeks to accomplish this purpose by a simplified sensing arrangement. As described more fully below, the presently preferred embodiment is capable of providing forced airflow control using a single sensor measuring condenser liquid refrigerant temperature at the inlet or upstream side of the flow control device for example, the thermal expansion valve. Compared with existing technology, the present invention uses a sensing arrangement which is simpler, easier to manufacture, install and maintain and thus lower in cost.
The present invention provides an improved forced air heat exchanging system in which a fan is positioned in the heating/cooling system to direct an airflow into heat exchange contact with a heat exchanger of the system. The fan has at least two speeds of operation and may provide either separate discrete speeds or a continuously variable speed, depending on the mode of operation of the system. A temperature sensor is coupled to the system so that it will sense the temperature of the liquid refrigerant, preferably at the inlet or upstream side of the flow control device. The metering device may be, for example, a variable expansion device or restricted orifice which delivers refrigerant to the evaporator coil.
A control circuit is coupled to the indoor fan and also to-the temperature sensor for controller the speed of the fan based on the temperature of the liquid refrigerant. Preferably the control circuit includes a microprocessor which processes the condenser liquid refrigerant temperature information to select the optimal fan speed. The microprocessor selects the optimal speed by using the liquid refrigerant temperature to extract information concerning diverse system functions ordinarily sent by separate sensors. For example, from the condenser liquid refrigerant temperature, the microprocessor is able to infer the outdoor ambient temperature and to infer whether the refrigerant compressor is running or not. This information is used to select the optimal indoor fan speed.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.